Ammonium nitrate propellants containing a nitro-aminocarboxy-alkali metal phenolate combustion catalyst



United States Patent Ofiiice Patented Apr. 19, 19,66

AMMGNIUM NITRATE PROPELLANTS CONTAIN= ING A. NITRO-AMINOCARBOXY-ALKALI METAL PHENOLATE (IOMBUSTION CATALYST Lionel A. Henderson, Columbus, Ind., assignor to Standard Gil Company, Chicago, 1th, a corporation of Indiana No Drawing. Original application Sept. 28, 1962, Ser. No. 227,048. Divided and this appiication June 27, 1963, Ser. No. 308,920

' Claims. (Cl. 149-19) This application is a division of Serial Number 227,048, filed Sept. 28, 1962.

This invention relates to the novel compounds nitroarninocarboxyalkali metal phenolates and to ammonium nitrate propellant compositions utilizing these compounds as a combustion catalyst.

In ammonium nitrate compositions formed from an oxidizable organic binder material which functions as a matrix for ammonium nitrate particles, it is necessary to promote the combustion of the mixture by means of a catalyst. Many catalysts are known for this purpose ranging from the very old inorganic chromium compounds such as ammonium dichromate to recently discovered alkali metal salts of certain organic acids and even completely organic compounds. The Prussian blues are of interest in high burning rate propellants, but these like the chromium compounds, produce reaction products which are solid mate-rials which cause severe nozzle erosion. The alkali metal catalysts react to form alkali metal carbonates which, while not particularly erosive, do result in an objectionable accumulation of ash in certain uses such as in gas generator use in connection with auxiliary power systems.

For propellant purposes, it is very desirable that the burning rate of the propellant show a minimum effect with variation in combustion chamber pressure. This effect of pressure on burning rate is commonly spoken of as the pressure exponent having the symbol n. The smaller the size of n, the less effect of pressure on the burning rate. The burning rate is affected by the temperature of the propellant mass. In general, the lower the temperature of the mass, the lower the burning rate. It is desirable that this temperature coefiicient, like the pressure exponent, below. The ultimate would be a situation in which the burning rate would be independent of pressure and temperature.

In general, the better known combustion catalysts have no influence on the characteristics of the propellant and function solely with respect to the rate of burning. Dependent upon the oxidizable organic binder material present, there commonly exists a problem with respect to ignition of the propellant at lower atmospheric temperatures. Frequently, it is necessary to introduce additives into the propellant composition to improve ignitability at these lower atmospheric temperatures which may be 2075 F. For some installations, it is necessary that the propellant deliver gas smoothly and uniformly for a long period of time. It is common to use low burning rate propellants in these situations. Unfortunately, with the prior art catalysts at low burning rates, it is difiicult to maintain smooth, uniform burning. Still more unfortunately, it is very difficult to overcome this problem by the addition of other compounds which im prove burning smoothness Without simultaneously harming the other characteristics of the propellant composition.

A .novel class of compounds has been discovered. These compounds act as combustion catalysts for ammonium nitrate propellant compositions. Compositions containing these compounds have superior ignitability characteristics at even the lowest of atmospheric temperatures. Propellant compositions containing these com pounds have superior, smooth, uniform burning characteristics at low burning rates. Propellant compositions containing these compounds give much less ash formation at a given burning rate than do the best previously known alkali metal containing organic compounds which function as combustion catalysts.

The novel class of chemical compounds of the invention may be broadly described as mixed salts of nitrocarboxyhydroxybenzene (nitromonocarboxylphenol or nitromonohydroxylbenzoic acid). In the compounds of the invention, the carboxyl group is reacted with an organic compound containing an amino group; the hydroxyl group is reacted with an alkali metal. The nitrosalicylic acids are especially suitable for the preparation of ammonium nitrate combustion catalysts. In addition to one or more nitro groups, the benzene nucleus may include alkyl substituents. It is to be understood that the novel class of compounds of the invention includes not only the compounds containing a single substituted benzene nucleus, but also two such nuclei which are joined by an. alkylene bridge. Illustrative of such a compound which can be used to produce an exceptional ammonium nitrate combustion catalyst is dinitromethylene disalicylic acid.

Broadly, the compounds of the invention fall into two sub classes: nitro-aminocarboxy-alkali metal phenolate or alkylene di(nitro aminocarboxy-alkali metal phenolate) where the alkylene group has 1-3 carbon atoms, i.e., methylene, ethylene or propylene. Any of the alkali metals may be used in forming the compounds of the invention. For use as a combustion catalyst, a sodium salt is especially suitable. Any organic compound containing an amino group may be used in forming the compound of the invention. The amines which contain carbon, hydrogen and nitrogen atoms and the amines containing carbon, hydrogen, oxygen and nitrogen atoms are especially suitable. The amines which are strongly basic are preferred when the composition needs exceptionable storage stability. Illustrative of especially suitable amines for the preparation of the catalyst used in the composition of the invention are ethylene diamine, monoethanolamine, diethylene diamine (piperazine) and guanidine.

Illustrative compounds of the invention based upon the reaction products of 3,5-dinitrosalicylic acid where the carboxyl group is in the 1 position are: the reaction. product with guanidine and sodium methoxide is 3,5-dinitro-1- guanidiniumcarboxy-Z-sodium phenolate. The reaction product with 1 mole of piperazine and 2 moles of sodium methoxide and 2 moles of acid is diethylene diamino bis- (carboxy-3,S-dinitro-Z-sodium phenolate). The reaction product with 1 mole of ethylene diamine, 2 moies of sodium methoxide and 2 moles of acid is ethylene diamino bis(carboxy-3,5-dinitro-2-sodium phenolate). The reaction product of 5,5 -n1ethylene-di(3,5-dinitrosalicylic acid) with guanidine and sodium methoxide is 5,5'-methylenedi 3 ,3'-nitro-1,1'-guanidiniumcarboxy-2,2'-sodium phenolate). It is to be understood that the scope of the com pounds of the invention are not limited to the illustrative compounds set forth above, but include the class as broad- 1y defined above.

When a compound of the invention is utilized as a catalyst for promoting the burning rate of ammonium nitrate propellant compositions, enough must be introduced into the composition to obtain a burning rate promotion. The amount of catalyst used is also influenced cent. .of the catalyst.

to be understood as weight percent.) With the thermoplastic matrix formers or binders obtained from cellulose esters and piasticizers therefor, between about 1 and 7% of catalyst produces satisfactory burning rates for typical military gas generation and rocketry usages.

The ammonium nitrate propellant composition utilizes as a catalyst broadly about O.ll weight percent of the above defined mixed salt; about -40 weight percent of oxidizable organic binder material; and ammonium nitrate as the major component. Other catalysts and additives may also be present.

The ammonium nitrate may be the high purity material commonly produced by synthetic plants today, or it may be technical grade containing small amounts of inorganic impurities. In addition to the ammonium nitrate, for special purposes, sodium nitrate or potassium nitrate may be present in an appreciable amount. The decomposition rate of the ammonium nitrate is influenced by the particle size. For gas generation purposes, the ammonium nitrate is finely divided. Particularly suitable ammonium nitrate will contain about 80 weight percent of material having a screen size greater than 80 mesh and smaller than 30 mesh. The more finely powdered ammonium nitrate is used where higher burning rates are desired. Usually the propellant composition will contain between about 60 and about 80 of ammonium nitrate. In all cases, the major component present in the composition is ammonium nitrate.

In order to permit the shaping of the ammonium nitrate composition into definite configurations, a matrix former or binder material is present. When ammonium nitrate decomposes, free-oxygen is released. The exist ence of this free-oxygen permits oxidizable organic materials to be used as the binders and thereby obtain additional gas production. These oxidizable organic materials may contain only carbon and hydrogen, for example, high molecular weight hydrocarbons such as asphalts or residuums, and rubbers, either natural or synthetic. Or, it may contain other elements in addition to carbon and hydrogen, for example, as in Thiokol rubber and neoprene. The stoichiornetry of the composition is improved, with respect to smoke production, by the use of organic materials containing combined oxygen as the binders. The binder or matrix former may be a single compound such as a rubber or asphalt or it may be a mixture of compounds. The mixtures are particularly suitable when special characteristics are to be imparted to the propellant which cannot be obtained by the use of a single compound.

Multi-component binder, or matrix former, consists of a polymeric base material and a plasticizer therefor. Particularly suitable polymeric base materials are cellulose esters of alkanoic acids containing from 2 to 4 carbon atoms such as cellulose acetate, cellulose acetate butyrate and cellulose propionate. The polyvinyl resins such as polyvinylchloride and polyvinyl acetate are good bases. Styreneacrylonitrile is an example of a copolymer which forms a good base material. Polyacrylonitrile is another suitable base material.

The plasticizer component of the binder also, preferably, contains combined oxygen. The oxygen may be present in the plasticizer as an ether linkage and/or hydroxyl and/ or carboxyl; also the oxygen may be present as a part of an inorganic substituent, particularly, a nitro group. In general, any plasticizer which is adapted to plasticize the particular polymer may be used in the invention. A single plasticizing compound may be used; more usually two or more compounds are used in conjunction. Examplary classes of plasticizers which are suitable are set out below. (It is to be understood that these classes are illustrative only and do not limit the types of organic compounds which may be used to plasticize the polymer.)

Di-lower alkyl-phthalates, e.g., dimethyl phthalate, di-

butyl phthalate, dioctyl phthalate and dimethyl nitrophthalate.

Nitrobenzencs, e.g., nitrobenzene, dinitrobenzene, nitrotoluene, dinitrotoluene, nitroxylene, and nitrodiphenyl.

Nitrodiphenyl ethers, e.g., nitrodiphenyl ether and 2,4-

dinitro-diphenyl ether.

Tri-lower alkyl-citrates, e.g., triethyl citrate, tributyl citrate and triamyl citrate.

Acyl tri-lower alkyl-citrates where the acyl group contains 2-4 carbon atoms, e.g., acetyl triethyl citrate and acetyl tributyl citrate.

Glycerol-lower alkanoates, e.g., monoacetin, triacetin,

glycerol tripropionate and glycerol tributyrate.

Lower alkylene-glycol-lower alkanoates wherein the glycol portion has a molecular weight below about 200, e.g., ethylene glycol diacetate, triethylene glycol dihexoate, triethylene glycol dioctoate, polyethylene glycol dioctoate, dipropylene glycol diacetate, nitromethyl propanediol diacetate, hydroxyethyl acetate and hydroxy propyl acetate (propylene glycol monoacetate).

Dinitrophenyl-lower alkyl-lower alkanoates, e.g., dinitrophenyl ethylacetate, and dinitrophenyl amyloctoate.

Lower alkylene-glycols wherein the molecular weight is below about 200, e.g., diethylene glycol, polyethylene glycol (200), and tetrapropylene glycol.

Lower alkylene-glycol oxalates, e.g., diethylene glycol oxalate and polyethylene glycol (200) oxalate.

Lower alkylene-glycol maleates, e.g., ethylene glycol maleate and bis-(diethylene glycol monoethyl ether) maleate.

Lower alkylene-glycol diglycolates, e.g., ethylene glycol diglycolate and diethylene glycol diglycolate.

Miscellaneous diglycollates, e.g., dibutyl diglycollate, dimethylalkyl diglycollate and methyl Carbitol diglycollate.

Lower alkyl-phthalyl-lower alkyl-glycollate, e.g., methyl phthalyl ethyl glycollate, ethyl phthalyl ethyl glycollate and butyl phthalyl butyl glycollate.

Di-lower alkyloxy-tetraglycol, e.g., dimethoxy tetraglycol and dibutoxy tetraglycol.

Nitrophenylether of lower alkylene glycols, e.g., dinitrophenyl ether of triethylene glycol and nitrophenyl ether of polypropylene glycol.

Nitrophenoxy alkanols wherein the alkanol portion is derived from a glycol having a molecular weight of not more than about 200. These may be pure compounds ofkadmixed with major component bis(nitrophenoxy) a ane.

In addition to the main components, i.e., ammonium nitrate binder and catalyst, the propellant composition may contain other components. For example, materials may be present to improve low temperature ignitability, for instance, oximes or asphalt; surfactants may be present in order to improve the adhesion of the nitrate and the binder also to improve the shape retention characteristics of the composition; burningrate promoters which are not considered to be true catalysts such as finely divided carbon may be present. Aromatic hydrocarbon amines such as toluene diamine, diphenyl amine, naphthalene dia-mine, and toluene triamine may be present. In order to improve storage stability, particularly at higher atmospheric temperatures, between about 0.1% and 1% of N-phenylmorpholine will be present.

A particularly good composition consists of cellulose acetate, about 612%; acetyltriethylcitrate, about 6-l2%; dinitrophenoxyethanol, about 6l2%; carbon, about 2-6%; toluene diamine, about 0.0-O.5%; N-phenylmorpholine, about 0.5%; catalyst, about 17% and the remainder ammonium nitrate.

It has been observed that propellant compositions containing one of the defined compounds of the invention and also an alkali metal barbiturate have exceptionally low pressure exponents and simultaneously very good temperature coefiicients. In general, these results are obtained using about equal weight amounts of the mixed salt "of this invention and alkali metal barbiturate with the total amount of the two compounds being between about 2 and 7 weight percent. An especially suitable combination is formed by monosodium barbiturate and the guanidine-sodiurn mixed salt of 3,5-dinitr-osalicyclic acid.

Although the burning rate at equal Weight content is somewhat lower than with the mononuclear compounds, the alkylene bridge dinuclea-r compounds give exceptionally low pressure exponents and very satisfactorily low temperature coefficients. For these reasons, compositions containing such mixed salts are suitable for military use where the composition will be fired over a wide range of atmospheric temperatures.

Illustrations The mixed salts of the invention are easily prepared by reaction in a common solvent for the particular acid, the particular amine and the alkali metal affording reactant. Methanol is. aparticularly good solvent reaction medium and a methoxideas the alkali metal affording reagent. A reaction rnedium can be readily selected wherein the product precipitates out in crystalline form. Purity of the product can be :determined easily by measuring the melting point of the crystals. It has been found by means of infrared inspection, regardless of which agent-amine or alkali metalis used first in the reaction, the final product has the amino group attached to the carboxy group and the alkali metal attached to the hydroxy group. Compounds were prepared by reacting equal moles of guanidine and sodium methoxide with 3,5-dinitrosalicyclic acid; reacting 2 mols of the 3,5-dinitrosalicyclic acid with 1 mol of diethylene diamine (piperazine); 2 mols of the 3,5-dinitrosalicyclic acid with ethylene diamine; 2 mols of guanidine with 1 mol of 3,5-dinitro-5,5-methylene disalicyclic acidin each instance the theoretical amount of sodium methoxide was added. In all cases, essentially the theoretical yield of mixed product was obtained in the form of crystalline solids. The position of the sodium and amino group was determined by infrared spectographic analysis of the crystalline solid.

The compounds were found to be eiiective burning rate catalysts for amornnium nitrate propellant compositions. Comparative compositions were prepared in a one quart laboratory mixer; each composition was mixed together for one hour at a temperature of about 212 F. Cellulose acetate, analyzing about 55% of acetic acid equivalent,- was used in conjunction with essentially pure dinitrophenoxyethanol and acetyl triethyl citrate plasticizers.

After the completion of the mixing, the pasty mass was compression molded into a slab /2" in thickness. The slab was permitted to cool to room temperature and sawed into strips for use in the Crawford bomb burning rate tests. Tests were carried out at different pressures in order to determine the pressure exponent n for each composition.

Tests were run to determine the temperature coeflicient of each composition. Temperature coeflicients were obtained at both constant pressure and constant nozzle size. In these tests, a propellant strand was brought to the desired test temperature by storage at that temperature until the entire mass of propellant was certain to be at the desired temperature. The ease of ignition and the smoothness and the uniformity of burning of the propellants was also observed.

In this series of tests, the component analysis of compositions tested was:

Percent Ammonium nitrate 64.62 Cellulose acetate 9.15 Acetyl triethyl citrate 10.15 Dinitrophenoxyethanol 9.30 Carbon black 3.60 Graphite 0.05 N-phenylmorpholine 1.25 Catalyst 1.88

Mark 6205 contained the sodium-guanidine mixed salt of 3,5-dinitrosalicylic acid. Mark 6206 contained the sodium-piperazine mixed salt of 3.,5-dinitrosalicylic acid. Mark 6207 contained the sodium-ethylene diamine mixed salt of 3,5-dinitrosalicylic acid. For comparison purposes, a composition was prepared, Mark 6209, containing monosodium barbiturate catalyst.

In the table below, there is set out the following: burning rate at 1,000 p.s.i.a. and 70 F, the pressure exponent n, the temperature coefiiieri't-tr, at constant pressure and the temperature coefiicient w at constant nozzle throat area and constant burning surface area.

Mark Burning n o w Rate The above data establish that the mixed salt compounds of the invention containing less than one-half the sodium metal content of sodium barbiturate have as good or better burning rates. These compositions also have better pressure exponents and as good or better temperature coefficients. The three compositions of the invention ignited easily at the lowest temperatures and burned smoothly.

A propellant composition, designated as Mark 6217, was prepared using as the catalyst the reaction product of guanidine, sodium methoxide and 3,3'-dinitro-5,5-methylene disalicylic acid in a mole ratio of 2:2: 1. This composition was prepared as described above using a 1 quart mixer wit-h a 40 minute agitation time. The component composition of composition Mark 6217 was:

Percent Ammonium nitrate 64.62 Cellulose acetate 9.15 Triethyl citrate 10.15 Dinit-rophenoxyethanol, pure 9.30 Carbon 3.60

Catalyst 1.88 N-phenylmorpholine 1.25 Graphite 0.05

This composition has a burning rate of 0.062 inch per second with a pressure exponent of 0.487. The temperature coefficient u was 0.075 and the temperature coefl-ieient 'n' was 0.148. By comparison with the characteristics shown in an earlier composition, Mark 6217 has a desirably low pressure exponent and desirably low temperature coeflicient, n'

Composition Mark 6214 included, as the catalyst, the mixed salt sodium guanidine dinitrosalicylate made as described previously and also monosodium barbiturate.

' The component formulation of Mark 6214 was:

Percent Ammonium nitrate 61.00 Cellulose acetate 9.79 Acetyl triethyl citrate 11.25 Dinitrophenoxyethanol (28% diether) 9.90 Carbon 3.00 Sodium guanidin-e dinitrosalicylate 2.06 Monosodium barbiturate 2.00 N-phenylmorpholine 0.50 Toluene diamine 0.50

Composition Mark 6214 gave a burning rate of 0.070 with a pressure exponent of 0.466. The temperature coetficient u was 0.100 and the temperature coefficient 11' was 0.19. The pressure exponent was unusually low considering the amount of monosodium barbiturate catalyst present; indeed this pressure exponent is markedly lower than that given by the catalysts set forth earlier. It is also evident that this particular composition has a desirably lower temperature coefiicient, 'rr than does the composi- 7 tion containing only monosodium barbiturate as a catalyst--Mark 6209.

Thus having described the invention, what is claimed is:

1. A propellant composition consisting essentially of about a 0.1-15 weight percent, as a combustion catalyst, of nitro-aminocarboxyaalkali metal phenolate, about 10 40 weight percent of oxidizable organic binder material; and about 60 to about 80 weight percent of ammonium nitrate.

2. The composition of claim 1 wherein said catalyst is 3,S-dinitro-1-guanidinium carboxy-Z-sodium phenolate.

3. The composition of claim 1 wherein said catalyst is diethylene diamino bis(carboxy-3,5-dinitro 2 sodium phenolate 4. The composition of claim 1 wherein said catalyst is ethylene diamino bis(l carboxy 3,5 dinitro 2 sodium phenolate).

5. The composition of claim 1 wherein said catalyst is 5,5 methylene di(3,3' nitro 1,1 guanidiniumcarboxy-2,2'-sodium phenolate).

5. The composition of claim 1 wherein said binder material consists of a cellulose ester of alkanoic acid having from 2 to 4 carbon atoms and a plasticizer adapted to plasticize said ester.

7. The composition of claim 1 wherein monoalkali metal barbiturate is present as a combustion catalyst and the amount of said barbiturate and said phenolate is about 2-7 weight percent.

8. A propellant composition consisting essentially of cellulose acetate, about 6-12%; acetyl triethyl citrate, about 6-12%; dinitrophenoxyethanol, about 612%; carbon, about 26%; toluene diamine, about (LO-0.5%; N- phenylmorpholine, about 0.5%; nitro-aminocarboxy-alkali metal phenolate, about 1-7%; and ammonium nitrate, 60-80%.

9. The composition of claim 8 wherein said phenolateis 3,5-dinitro-l-guanidiniumcarboxy-Z-sodium phenolate,

10. The composition of claim 8 wherein said phenolate is 5,5 methylene di(3,3 nitro 1,1 guanidiumcarboxy-2,2-sodium phenolate).

References Cited by the Examiner UNITED STATES PATENTS 2,929,698 3/1960 Audrieth et a1. -l49l05 2,969,638 1/1961 Sammons 149l9 3,138,497 6/1964 Kennedy l49--19 REUBEN EPSTEIN, Primary Examiner.

CARL D. QUARFORTH, Examiner. 

1. A PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF ABOUT A 0.1-15 WEIGHT PERCENT, AS A COMBUSTION CATALYST, OF NITRO-AMINOCARBOXY-ALKALI METAL PHENOLATE, ABOUT 1040 WEIGHT PERCENT OF OXIDIABLE ORGANIC BINDER MATERIAL; AND ABOUT 60 TO ABOUT 80 WEIGHT PERCENT OF AMMONIUM NITRATE. 